This invention relates to wavelength division multiplexed (WDM) optical systems, and more particularly to method and apparatus for a dense WDM (DWDM) optical system.
In optical transmission systems the capability to determine the connectivity of network elements (NE) is important in performing equipment inventory management, fault isolation, and automated provisioning of the system. In a DWDM system, which typically carries 33 or more multiplexed channels of information over a single fiber, this capability would normally require an optical demultiplexer in each NE in order to access the information carried by the channels. This information would then be used to determine the connectivity of the NE. However, optical demultiplexers are relatively expensive components, and therefore, to include them in an NE solely for determining the connectivity of the NE where they otherwise would not be required is undesirable. It appears then, that an alternative technique of providing the capability to determine the connectivity of an NE would be useful.
An object of the present invention is to provide improved method and apparatus for ancillary data in a WDM optical transmission system.
The present invention provides a low bit rate data channel for carrying ancillary data between a channel wavelength source and an optical NE in a WDM system. The low bit rate data channel, hereinafter called a WaveID, is carried by a sub-carrier frequency signal that has been modulated by the ancillary data. The modulated sub-carrier frequency signal is used to modulate an optical data; signal. The WaveID of each channel is orthogonal to other WaveIDs. That is, for an optical signal that is comprised of a plurality of modulated optical data signals that are each of a different channel wavelength, each WaveID can be detected independently from other WaveIDs.
According to one embodiment of the present invention each WaveID can carry ancillary data that includes channel source identification information, such as a unique channel identifier that uniquely identifies the wavelength source. Further to this end, the WaveID could carry such ancillary data as: Internet protocol (IP) address of the source, physical location identifier of the source, working or protection channel identification, payload format and bit rate identifiers, and other such information as dictated by future requirements.
The WaveIDs can be detected by an NE equipped with a tap coupler, a photo detector, and a WaveID detector. By tapping an incoming optical signal: and detecting the set of WaveIDs present, an NE can determine the wavelength sources to which it is connected via the network. This allows the NE to verify or discover its connectivity to the network. This capability is particularly attractive for Metro Optical Networks (MON) where inexpensive techniques of optical connectivity verification are required.
An advantage of the present invention is that it does not require optical demultiplexing of the channel wavelengths in order to identify the channel wavelength sources. Consequently, adding optical demultiplexors in order to perform channel source identification is not necessary. This leads to a relatively inexpensive technique of channel source identification that is useful in determining the connectivity of an NE in a DWDM system.
According to an aspect of the present invention there is provided an apparatus for ancillary data in a wavelength division multiplexed system comprising: a modulator for modulating a sub-carrier frequency signal with the ancillary data; an intensity modulator for amplitude intensity modulating an optical data signal: with the modulated sub-carrier frequency signal; al tap coupler for tapping a portion of the amplitude intensity modulated optical signal; an opto-electronic convertor for converting the tapped portion of the optical signal to an electrical signal; and a detector for detecting the modulated sub-carrier frequency signal from the electrical signal, and for detecting the ancillary data from the modulated sub-carrier frequency signal.
According to another aspect of the present invention there is provided an encoder for ancillary data in a wavelength division multiplexed system comprising: a modulator for modulating a sub-carrier frequency signal with the ancillary data; and an intensity modulator for amplitude intensity modulating an optical data signal with the modulated sub-carrier frequency signal.
According to another aspect of the present invention there is provided a decoder for extracting ancillary data from an optical data signal that has been amplitude intensity modulated by a modulated sub-carrier frequency signal that has been modulated by the ancillary data in a wavelength division multiplexed system, comprising: a tap coupler for tapping a portion of the modulated optical data signal; an opto-electronic convertor for converting the tapped portion to an electrical signal; and a detector for detecting the modulated sub-carrier frequency signal from the electrical signal, and for detecting the ancillary data from the modulated sub-carrier frequency signal.
According to yet another aspect of the present invention there is provided a method of identifying channel sources in a wavelength division multiplexed system comprising the steps of: at a first node in the system, modulating a sub-carrier frequency signal with the ancillary data; at the first node, amplitude intensity modulating an optical data signal with the modulated sub-carrier frequency signal; at the first node, transmitting the modulated optical data signal onto an optical fiber; at a second node in the system, tapping a portion of the modulated optical data signal from the optical fiber; at the second node, converting the tapped portion to an electrical signal; at the second node, detecting the modulated sub-carrier frequency signal from the electrical signal; and at the second node, detecting the ancillary data from the modulated sub-carrier frequency signal.
According to still another aspect of the present invention there is provided an amplitude intensity modulated optical signal for conveying ancillary data in a wavelength division multiplexed system comprising:
pulse modulated light of a constant wavelength that has been modulated at a first bit rate by a first sequence of data symbols; and an amplitude intensity modulation of the pulse modulated light at a sub-carrier frequency that is less than the bit rate of the optical data signal divided by two and where the sub-carrier frequency has been modulated by ancillary data represented by a second sequence of data symbols, wherein the second sequence of data symbols has a bit rate that is at least eight orders of magnitude lower than the first bit rate.
According to still another aspect of the present invention there is provided an apparatus for ancillary data in a wavelength division multiplexed system comprising: a data source for providing the ancillary data wherein the ancillary data includes channel source identifying information; and means for including the ancillary data in an optical data signal, wherein the optical data signal is amplitude intensity modulated by a signal that has been modulated by the ancillary data.